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Home battery planner

Compare home battery sizes from 0 to 20 kWh and see how much each extra kilowatt hour adds to your self-sufficiency. Runs in your browser.

Annual electricity use (kWh)

Solar system size

Region

Specific yield (kWh per kWp and year)

A heat pump is included in this figure

Battery powerContinuous charge and discharge power of the battery system.

Size to inspectDrag to compare sizes; the highlighted bar in the chart follows.

Your estimate

Sweet spot for your numbers

Self-sufficiency without battery

With the inspected size

Gain from storage

Use of the battery

Energy shifted

Rule of thumb

Self-sufficiency per battery size (kWh)Sweet spotInspected size

An estimate for planning, not an offer or a yield guarantee. Nothing you enter is sent anywhere.

How the calculation works

For every battery size from 0 to 20 kWh, the planner simulates a representative day for each month in quarter-hour steps, with the same solar and household profiles as the solar calculator, and adds up the year. The sweet spot is the largest size at which one more kilowatt hour still raises self-sufficiency by at least two percentage points. Beyond that, each extra kilowatt hour costs as much as the first ones but is cycled far less often.

The battery charges only from solar surplus and discharges to cover the house; round-trip efficiency is set at 90 percent.
Full cycles per year are the energy discharged divided by the usable capacity. Below about 200 cycles a year, a battery is mostly waiting.
The rule of thumb shown alongside is about 1 kWh of usable capacity per 1,000 kWh of annual use, capped at about 1.5 kWh per kWp.

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